Yah, JFJ, sorry, I thought it was about a 5th era, and its actually about a future era. Cos the 5th era doesn`t exist. You could cramm the techs from 2 eras into 1 for all you want, but there can still be only 4.
JFJ - of course you can shuffle techs the way you see fit, and create even a near and far future eras if you want, with cramming the ancient and medieval in the first era, and industrial and modern in the second. There are tons and tons of custom tech-trees that do that sort of thing....
This is like someone from the present would ask: "hey, d`ya think I could get those horses to pull my wagon?"